Do recovering drug addicts have emotion problems?

So my friend is a recovering drug addict it's pretty wierd because in the 7th grade he was this anti social quite kid always depressed he was one of the nicest guys you'll meet and never wanted to fight kids. Then he said he started messing with pills in 10th grade like anti depressants, ecstasy, and he seemed like he wasn't so depressed anymore actually happier. Then he had a gun pulled to his face and that's when everything went down hill he started doing pcp ketamine really big time dissociatives drugs. The first thing I noticed was he was emotionless then he wouldnt be able to understand simplest things and he could barely make a sentence and always struggled to find the right words to say. He also pick fights with almost anyone. He's supposedly already has recovered. He has a certificate saying he's gone through rehab and another one for drug therapy. He seems like he's smarter he speaks much faster tho. He knows how to make a sentence easy and he's smart again like he use to be and logically understands most things. But emotionally he doesn't. He tells me all the time he doesn't understand emotions. He's super nice and actually kinda makes him seem insane. He always happy with everything. He always Askes me how to do things right in a relationship his girlfriend loves him but it seems like he doesn't love her. He sometimes doesn't understand why his girlfriend tells him things like I love and I miss you he thinks she's crazy. But he obviously doesn't understand emotions and can't obviously use his own emotions. He thinks the only emotion he feels is happiness which is pretty crazy. Me and him were Dissecting a baby pig in anatomy and the crazy thing was he laughed with happiness in his laughter when he cut off the pigs head. Idk he seems to have problems with his emotions can any tell what's wrong with him? I hope I gave enough information to get a concept of what's wrong with him.